Low Dose Supplementation to Improve Anticoagulation Control With Oral Vitamin K as an Adjuvant to Warfarin Therapy

Ottawa Hospital Research Institute100 enrolled

Overview

The main objective of this study is to assess the effectiveness of low dose Vitamin K1 (200 micrograms per day) at improving anticoagulation control in unstable patients on warfarin. This study will also aim to look at effectiveness in the context of genes known to influence warfarin metabolism, variability in the consumption of Vitamin K rich foods, and patient knowledge about warfarin anticoagulation -- factors which have been associated with anticoagulation control and which can influence the effectiveness of this intervention in clinical practice.

A double-blinded placebo controlled pilot RCT assessing the effectiveness of daily supplementation with low dose Vitamin K1 (200 micrograms per day) against placebo at improving anticoagulation control. Previous studies assessing the efficacy of this intervention have been small and further trials are required to evaluate the true effectiveness and safety profile. Furthermore the impact of genetic polymorphisms, known to impact warfarin metabolism, on the effectiveness/safety of this intervention will also be assessed in this study. Demographic and clinical variables as well as potential confounding variables such as variable dietary Vitamin K intake, concomitant interacting medications, and anticoagulation knowledge will be assessed in this study. Given that this is a pilot study we will be looking at recruitment numbers and necessary parameter estimates to determine the number of patients available at our institution for the study. Power analysis will be performed to evaluate the treatment effect size between the placebo and intervention groups.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

TRIPLE

Enrollment

100

Conditions

Interventions

Vitamin K1 (Phytonadione)DIETARY_SUPPLEMENT

Vitamin K1 tablets (100 micrograms per tablet) will be taken by patients randomized to the Vitamin K arm. Dosage is two tablets per day (200 micrograms per day) to be taken with warfarin for the 6 month study period.

PlaceboDIETARY_SUPPLEMENT

Lactose-based placebo tablets (identical in appearance to the Vitamin K1 tablets) will be taken by patients randomized to the placebo arm. Dosage is two tablets per day to be taken with warfarin for the 6 month study period.

Eligibility

Sex: ALLMin age: 18 Years

Medical Language ↔ Plain English

Inclusion Criteria: * \>= 18 years old * Have been on warfarin anticoagulation for at least 9 months * Have an INR target range of 2.0-3.0 * Have "unstable" anticoagulation control, defined as in the preceding 6 months having at least 3 INRs out of range (\>= 3.2 or =\<1.8) or at least 3 warfarin dose changes * Have anticoagulation managed by the Ottawa Hospital Thrombosis Clinic * Able to provide written, informed consent Exclusion Criteria: * Anticipated interruption or termination of warfarin anticoagulation in the next six months for a period of 1 week or greater * Patient instability in the preceding six months suspected to be due to a) Interruption of warfarin therapy for a period of 1 week or more or b) Significant non-compliance (assessed from patient record) * Possess a known allergy to Vitamin K or lactose based placebos * Unable/Refusal to provide written, informed consent

Outcomes

Primary Outcomes

Anticoagulation control -- Point estimates (and standard deviations) for the following variables: Percent time in therapeutic range, standard deviation of INRs, number of INRs outside of therapeutic range, and number of dose changes

Time frame: At study initiation (for the six month pre-intervention period) and at study completion (after the six-month intervention period)

Recruitment Numbers -- Number of patients deemed eligible, Number of patients solicited, Number of patients screened, Number of patients enrolled, and Number of enrolled patients lost to follow-up

Time frame: Monthly

Secondary Outcomes

Bleeding Events -- Both major and minor as defined by the International Society on Thrombosis and Haemostasis (ISTH) criteria

Time frame: Over 6 month study period

Recurrent thrombosis

Time frame: Over six month study period